Changes in arterial autoregulation in dependence on the level of blood pressure and its circadian rhythm

Aim. The aim of the study was to investigate the effects of blood pressure and its circadian rhythm on cerebrovascular reactivity (CVR). Transcranial duplex scanning (TKDS) of the middle cerebral artery (MCA) and the measurement of blood pressure (BP) (ambulatory BP monitoring and office BP control) were performed in 124 patients with essential hypertension aged 55.2±12.3 years. TKDS was performed with hyperoxia and hypercapnia tests. In patients with abnormal reverse reaction in the presence of hyperoxia, BP was higher (average daily BP: 142.2±12.6/87.4±10.1 mm Hg), and the daily index of SBP was lower (6.0±1.2%) compared with those in patients in whom only hyperoxic reaction was impared (average daily BP: 136.2±7.6/83.4±10.3 mm Hg, p=0.011/0.016; SBP day/night index: 14.2±2.6%, p=0.0007). Patients with abnormal circadian BP rhythm (non-dippers and night-pickers) with high indexes at night had statistically significant differences in the following CVR parameters: the rate of blood flow velocity change, blood flow velocity in the presence of hyperoxia and hypercapnia, and time index of linear blood flow velocity in the presence of hypercapnia. Patients with reverse reaction during hyperoxia had higher office BP, higher values of ABPM, and lower daily index; there was a statistically significant correlation between the levels of blood pressure and parameters of CVR. Patients with reverse CVR reactions (non-dippers and night-picker) had three-fold rate of abnormal BP circadian rhythm compared with patients who had normal type of CVR reactions.